1. Field of the Disclosure
The disclosure relates to high power fiber laser systems and, more particularly, to high power fiber laser systems configured with a side-pumping arrangement.
2. Prior Art Discussion
High power fiber lasers and amplifiers have one or more gain blocks each typically including a multi-clad active fiber and a pump-light delivery passive fiber which are arranged in a side-pumping scheme. Completing the configuration of the gain block, such as a fiber amplifier, are typically an input passive fiber launching signal light into the active fiber and output passive fiber receiving the amplified signal light therefrom.
FIG. 1 illustrates one of the known configurations of a gain block 10 having a side-pumping arrangement, which includes a pump multi-mode passive fiber 12, a doped fiber 16, which is typically, but not necessarily, is a multimode fiber capable of supporting a fundamental mode at the desired wavelength, and a reflective coating 18. The pump and active fibers have respective stretches operatively connected to one another and defining a coupling region 14. The structure of FIG. 1 is further referred to as a twin configuration.
The active and pump fibers 16 and 12, respectively, are drawn from respective pre-forms and further guided through a furnace so as to draw respective fibers, which later are surrounded by reflective coating 18. Upon winding a twin on a reel, it is ready for use by splitting fibers 12 and 16, respectively, so that pump fiber 12 is operatively connected to a light source and doped fiber 16 to a single mode passive fiber, provided a gain block is configured as a fiber amplifier. Otherwise, the twin may be used as a seed source provided with a resonant cavity in a well known manner. Since the pumping is typically performed in opposite directions, the fibers are separated at the opposite ends of coupling region 14.
In operation, pump light, launched by passive pump delivery fiber 12, starts propagating into doped fiber 16 through end portions A of coupling region 14. As pump light propagates along coupling region 14, its major part is gradually absorbed by gain medium of a core 20 of doped fiber 16 so as to amplify signal light launched from input passive fiber 22 into core 20. The amplified signal light is further coupled into an output passive fiber 24 which guides it, for example, to a next gain block or any other recipient of the amplified light.
The practice shows that high power fiber laser systems based on one or more gain blocks similar to one of FIG. 1 may experience undesirable dispersion of high pump power at regions A which are located next to the beginning/end of coupling region 14. Even more vulnerable regions include the remaining ends of reflective coating 18 after its end portions are removed during the split of the fibers. The heat generated by such high pump powers frequently causes burning of reflective coating 18 which leads to a quick destruction of the twin structure and, thus, of the gain block.
A need therefore exists for a high power fiber laser system having at least one twin structure which is capable of withstanding high pump powers.
Still a further need exists for a process of manufacturing fibers providing the protection of high power fiber lasers of the type disclosed immediately above.